1. Field of the Invention
The invention relates to melt-processible, highly-neutralized ethylene, C3 to C8 α,β ethylenically unsaturated carboxylic acid copolymers and process for making them. It relates to such copolymers, neutralized to greater than 90%, particularly to those neutralized to nearly to or to 100%. These copolymers are made by incorporating a sufficient amount of specific organic acid (or salt) into the copolymer before neutralization to the high level.
The invention particularly relates to melt-processible, highly-neutralized (greater than 90%) polymer comprising (1) ethylene, C3 to C8 α,β ethylenically unsaturated carboxylic acid copolymers that have their crystallinity disrupted by addition of a softening monomer or other means, and (2) sufficient amount of a non-volatile, non-migratory agent such as an organic acid (or salt) selected for its ability to substantially or totally suppress the ethylene crystallinity. Agents other than organic acids (or salts) may be used.
The invention also relates to thermoplastics that, when molded into spheres, have a coefficient of restitution of at least 0.785 (measured by firing a sphere of the thermoplastic at an initial velocity of 125 feet/second against a steel wall positioned 3 feet from the point where initial velocity and rebound velocity are determined and by dividing the rebound velocity by the initial velocity) and an Atti compression of no more than 100.
These copolymers are useful in making molded products such as golf ball components, thermoplastic shoe soles for cleated footwear, and resilient foams for sporting goods. They are particularly useful in the manufacture of one-, two-, and three-piece and multi-layered golf balls. The invention particularly relates to the spherical components (cores, centers, and one-piece balls) having a coefficient of restitution of at least 0.785 when measured at 125 feet/second and Atti compressions of 100 or less.
2. Description of Related Art
Typical premium golf balls include three-piece balls, two-piece balls and multi-layered balls. “Three-piece” balls typically have a spherical molded center, elastomeric thread-like material wound around the center, and either a thermoplastic or thermoset cover. “Two-piece” balls typically have a spherical molded core covered with a thermoplastic material. “Multi-layered” balls typically have a spherical molded core and one or more intermediate layers or mantles between the core and a cover.
Three-piece centers and two-piece and multi-layer cores have traditionally been made using a thermoset rubber such as polybutadiene rubber. With thermoset rubber, complex multi-step processes are needed to make cores and centers and scrap cannot be recycled. Attempts to solve these difficulties by substituting a thermoplastic for the thermoset have had limited success. Also, attempts to make premium one-piece balls have been unsuccessful. See U.S. Pat. No. 5,155,157, UK Patent Application 2,164,342A and WO 92/12206. Balls, cores and centers made based on these references have a high cost and lack properties such as durability, softness (low Atti compression), and resilience to make them useful in premium balls.
One thermoplastic that has found utility in golf ball components and other applications for a long time are ionomers of copolymers of alpha olefins, particularly ethylene, and C3-8 α,β ethylenically unsaturated carboxylic acid. U.S. Pat. No. 3,264,272 (Rees) teaches methods for making such ionomers from “direct” acid copolymers. “Direct” copolymers are polymers polymerized by adding all monomers simultaneously, as distinct from a graft copolymer, where another monomer is grafted onto an existing polymer, often by a subsequent free radical reaction. A process for preparing the acid copolymers on which the ionomers are based is described in U.S. Pat. No. 4,351,931.
The acid copolymers may contain a third “softening” monomer that disrupts the crystallinity of the polymer. These acid copolymers, when the alpha olefin is ethylene, can be described as an E/X/Y copolymers wherein E is ethylene, X is the α,β ethylenically unsaturated carboxylic acid, particularly acylic and methacrylic acid, and Y is the softening co-monomer. Preferred softening co-monomers are C1 to C8 alkyl acrylate or methacrylate esters. X and Y can be present in a wide range of percentages, X typically up to about 35 weight percent (wt. %) of the polymer and Y typically up to about 50 weight percent of the polymer.
A wide range of cations is known for neutralizing acid moieties in the acid copolymer. The degree of neutralization is known to vary over a wide range. Typical cations include lithium, sodium, potassium, magnesium, calcium, barium, lead, tin, zinc, aluminum, and combinations of such cations. Neutralization to 90% and higher, including up to 100%, is known, but such a high degree of neutralization results in a loss of melt-processibility or properties such as elongation and toughness. This is particularly so for copolymers with high acid levels and when using cations other than barium, lead and tin to neutralize the copolymer.